According to the GAO, “the F-35 fighter plays a key role in U.S. defense strategy. As of October, the United States and international partners had fielded more than 435 of an expected 3,300 aircraft. We testified that DOD faces challenges keeping the growing fleet ready to perform its mission, largely due to insufficient planning. Challenges include:

• Spare parts shortages: F-35s were unable to fly about 30% of the time due to a lack of spare parts from May-November 2018
• Poor performance of the information technology system used to sustain the aircraft: It requires manual workarounds and has data inaccuracies
• Long-term sustainment planning: Looking to the future, DoD lacks information about the technical characteristics and costs of the F-35 to effectively plan for long-term sustainment.

As a result of these challenges, F-35 performance has not met warfighter requirements. While DOD works to address these issues, it must also grapple with affordability. DOD has determined that it will need to significantly reduce F-35 sustainment costs—by 43 percent per aircraft, per year in the case of the Air Force—in order for the military services to operate the F-35 as planned.

Continued attention to GAO's recommendations in these areas will be important as DOD takes actions to improve F-35 sustainment and aircraft performance for the warfighter….We have 21 open recommendations to address these issues.”